How to go about offer shopping. Any tips and insights.

So I have around 60 days of np. I have an offer but the hr released an offer with a lower than agreed upon number and mentioned that once you reach the end of np we will increase it to the agreed upon number.

Is this a common practice?

Also I am in a SBC and cracking other SBCs seems easy.But I am not getting calls from product based companies.

Should I disclose to the HR if I have multiple offers as well?